When a dinner bill comes it has the Sub Total and Tax above the Total. Enter both of those values in the specified fields and press what % you would like to tip. Tipbox outputs Tip Amount and Total, the two values needed to fill in the rest of the bill. Very Easy.
If you know what you want to tip, but are curious what % it is, use the Tip Amount field and the ?% button.
Tipbox does not factor the tax into the tip. If you happen to want to tip for the tax, enter the total into the Sub Total field and leave the Tax field blank.